This invention relates to an improved flash-butt welder of economical construction which ensures uniformly high quality welds on band saw stock. The most important factors in obtaining high quality welds are precise alignment of the edges being welded and accurate control of the relative rate of advance of the work pieces during the flashing and upset movement thereof.
There are a number of prior art patents which disclose flash-butt welders of this general type. These include U.S. Pat. Nos. 2,860,231; 3,370,149 and 4,235,115. The earliest of these prior patents to Stone shows a relatively complex combination of a pneumatic drive cylinder which rotates a bell crank opposed by a cam follower linkage 50 which rides on a cam plate 38. A separate trip cylinder pivots the linkage at a particular point in the welding cycle so that during the upset phase of the cycle the full force of the main cylinder will drive the movable platen.
The Allen U.S. Pat. No. 3,370,149 also discloses a main pneumatic cylinder which drives a lever 26. The pivotable movement of the lever is opposed by a quite complex bell crank and snubbing cylinder. The bell crank carries a cam follower which rides upon a cam surface formed on the outer end of the lever.
The Gordon U.S. Pat. No. 4,235,115 discloses the use of a power spring 40 to drive a pivotable lever 20 and thereby advance a movable platen 16 during the welding sequence. A snubbing cylinder 60 and cam 42 oppose the movement of the lever 20 which carries a drive wheel 50 carried on a toggle-type link 52.
It will be noted that each of the above patents involves, in various ways, a cam of diminishing radius which controls the rate of advance of the movable work-holding platen. Each of the cams has a drop-off surface at which there is a transition in acceleration as a cam follower rolls off the gradually diminished cam surface. The Stone patent is somewhat different in that a separate trip cylinder actually pivots the cam follower out of contact with the cam surface.
In the present flash-butt welder construction control of the welding cycle is independent of the particular configuration of a precut cam.
The principal object of this invention is to provide a flash-butt welder having improved construction and performance characteristics.
A further object of this invention is to provide a flash-butt welder of compact construction which is especially adapted for butt welding band saw blades.
Another object of this invention is to provide a flash-butt welder of economical construction designed to provide more effective transition from the flashing to the upset movement of the workpieces being welded.